It is desired to fabricate yarns that are coated in ceramic or other particulate materials and which are suitable for the manufacture of fabric which could be used in a variety of ways. For example, it is known that appropriately processed ceramic “nanoparticles” of titanium dioxide (TiO2, or “titania”) and aluminum oxide (Al2O3, or “alumina”), which have very high surface areas for their weight, are known to be absorbent of biohazardous materials. See Koniz, “Self-Detoxifying Textiles for Chemical and Biological Agent Protection”, a paper presented in 2006 at a conference entitled TechTextil. Koniz also suggests that certain polyoxometalate and chloramide particles may be useful for similar purposes.
Thus, a yarn comprising a polymer core and a durable coating of these nanoparticles that is suitable for manufacture of fabric for use in garment manufacture would be highly desirable in manufacture of protective clothing, tents, buildings, and the like.
Polymer yarns might also usefully be coated with other types of particles for other purposes; for example, it might be possible to make a yarn with an electrically-conductive outer sheath made up of deposited conductive powder. Such a yarn would have a variety of uses, such as manufacture of conductive cloth for shielding electronic components worn on one's person from EMI (electromagnetic interference) and RFI (Radio Frequency interference).
In further examples of the use of the invention, yarns coated by refractory particulate materials or advanced engineering ceramics could be used to manufacture abrasion-resistant fabrics, fire retardant fabrics, sensing fabrics, electronic fabrics, piezoelectric fabric, self cleaning and/or self repairing fabric, or all sort of intelligent fabrics. Yarns coated in retroreflective glass beads could be used to make reflective fabric, for safety garments, fabric signage, and the like.
It is also desired to coat metallic wires with a layer of polymer and then a layer of particulate material. If an electrically-conductive particulate were used such that a continuous conductive coating were formed, a coaxial wire would be provided, which could be used to carry small signals, or as a capacitor. The dielectric constant of the polymer layer could be controlled by addition of, for example, mica or ceramic particles to the polymer layer. Such a composite coaxial wire would have many uses.
Consequently, it is desired to provide a method for efficiently and reliably coating yarns with very fine, “nano-sized” particles. (It will be appreciated that use of the term “nano-sized” is not intended to imply any limitation on the invention per se.) Such yarns and the coatings thereon would need to be suitably durable for their desired use, for example, so as to be processed into cloth from which garments could be made, or otherwise employed to form the final product, and to withstand ordinary wear and tear due to use and cleaning thereafter.
One attempt to make a powder-coated yarn of which the present inventors are aware involved coating a polymer precursor strand with a UV-curable resin, spraying the coated strand with the desired powders, and then exposing the sprayed strand to UV, to cure the resin coating and fix the powder particles thereon. This was unsuccessful for a variety of reasons. The powder did not coat the surface uniformly, the powder was very inefficiently applied, and the coating was insufficiently durable. Furthermore, as the excess powder was contaminated with UV-curable resin, the recovery of excess powder was very difficult.